Whie the highly classified Area 51 might be the United States' most famous military base it's far from the country's most secretive.
The covert Air Force base, located in Lincoln County, Nevada, was opened during the Cold War in 1955 but its existence was only officially acknowledged by the CIA in August 2013.
Despite this, Area 51 has long been notorious, largely on account of its frequent association with alien mythology and UFO conspiracy theories.
What precisely goes on inside the base is kept extremely secret, but it's thought the US military uses the site to develop cutting-edge aircraft.
Members of the public are kept away from the compound by warning signs, electronic surveillance, and patrols of armed guards.
It is also illegal to fly over Area 51, although the site is now visible on satellite images.
The secrecy surrounding the base has fanned the flames of the aforementioned conspiracies about aliens and UFOs.
One of the most famous is the claim that the site hosts an alien spacecraft and the bodies of its pilots after they crashed at Roswell, New Mexico, in 1947.
Others claim to have seen UFOs above or near the site, while some say they have been abducted by aliens, and even experimented on, before being returned to Earth.
While the fascination with Area 51 is sure to continue, the US military has a number of other classified, lesser-known bases built during the Cold War era that are shrouded in even more mystery as to their actual purpose and function.
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